Astraea was treated as a section of Croton by G. L. Webster (1993). However, the molecular phylogeny of P. E. Berry et al. (2005) showed that it represents a lineage distinct from Croton. Morphological characters that support this separation include the markedly rectangular seeds, the often deeply lobed leaves, and the mixture of simple and stellate hairs. Astraea is most diverse in southeastern Brazil.